Problem: $7de + 9df + 2d - 2 = 2e - 8$ Solve for $d$.
Combine constant terms on the right. $7de + 9df + 2d - {2} = 2e - {8}$ $7de + 9df + 2d = 2e - {6}$ Notice that all the terms on the left-hand side of the equation have $d$ in them. $7{d}e + 9{d}f + 2{d} = 2e - 6$ Factor out the $d$ ${d} \cdot \left( 7e + 9f + 2 \right) = 2e - 6$ Isolate the $d$ $d \cdot \left( {7e + 9f + 2} \right) = 2e - 6$ $d = \dfrac{ 2e - 6 }{ {7e + 9f + 2} }$